The present invention relates to peptide nanostructures, articles, devices and methods of generating and using same.
Nanoscience is the science of small particles of materials and is one of the most important research frontiers in modern technology. These small particles are of interest from a fundamental point of view since they enable construction of materials and structures of well-defined properties. With the ability to precisely control material properties come new opportunities for technological and commercial development, and applications of nanoparticles have been shown or proposed in areas as diverse as micro- and nanoelectronics, nanofluidics, coatings and paints and biotechnology.
It is well established that future development of microelectronics, magnetic recording devices and chemical sensors will be achieved by increasing the packing density of device components. Traditionally, microscopic devices have been formed from larger objects, but as these products get smaller, below the micron level, this process becomes increasingly difficult. It is therefore appreciated that the opposite approach is to be employed, essentially, the building of microscopic devices from a molecular level up, primarily via objects of nanometric dimensions. Self-assembled nanoparticles, such as nanotubes and nanospheres, allow controlled fabrication of novel nanoscopic materials and devices. Such nanostructures have found use in areas as diverse as micro- and nanoelectronics, nanofluidics, coatings and paints and biotechnology.
In particular, wire-like semiconducting nanostructures. Most have attracted extensive interest over the past decade due to their great potential for addressing some basic issues about dimensionality and space confined transport phenomena as well as related applications. Wire-like semiconducting nanostructures often have distinctive properties and can be used as transparent conducting materials and gas sensors. For example, fluorine-doped tin oxide films are used in architectural glass applications because of their low emissivity for thermal infrared heat. Tin-doped indium oxide films can be used for flat panel displays due to their high electrical conductivity and high optical transparency.
In the field of magnetic recording, wire-like nanostructures can be used as magnetoresistive read transducers. It has been well known that the magnetoresistive sensors are capable of reading information from the surface of magnetic recording media at high linear densities. The magnetoresistive sensors sense magnetic signals by way of the electrical resistance change of magnetoresistive elements that varies as a function of the strength and orientation of the magnetic flux sensed by read or magnetoresistive elements. The use of nanoscale elements in such sensors significantly increases the capability of retrieving accurate information from highly dense magnetic media.
In the field of displays, much effort has been devoted to developed electrophoretic displays. Such displays use a display medium comprising a plurality of electrically charged particles suspended in a fluid. Electrodes are provided adjacent the display medium so that the charged particles can be moved through the fluid by applying an electric field to the medium. In one type of such electrophoretic display, the medium comprises a single type of particle having one optical characteristic in a fluid which has a different optical characteristic. In a second type of such electrophoretic display, the medium contains two different types of particles differing in at least one optical characteristic and in electrophoretic mobility.
Numerous configurations have been proposed and applied for the construction of nanostructures. The most widely used building blocks of nano-materials and nano-devices are the fullerene carbon nanotubes. Two major forms of carbon nanotubes exist, single-walled nanotubes (SWNT), which can be considered as long wrapped graphene sheets and multi walled nanotubes (MWNT) which can be considered as a collection of concentric SWNTs with different diameters.
SWNTs have a typical length to diameter ratio of about 1000 and as such are typically considered nearly one-dimensional. These nanotubes consist of two separate regions with different physical and chemical properties. A first such region is the side wall of the tube and a second region is the end cap of the tube. The end cap structure is similar to a derived from smaller fullerene, such as C60.
Carbon nanotubes produced to date suffer from major structural limitations. Structural deviations including Y branches, T branches or SWNT junctions, are frequent results of currently used synthesis processes. Though such deviations in structure can be introduced in a “controlled” manner under specific conditions, frequent uncontrollable insertion of such defects result in spatial structures with unpredictable electronic, molecular and structural properties.
Other well-studied nanostructures are lipid surfactant nanomaterials (e.g., diacetylene lipids) which self-assemble into well-ordered nanotubes and other bilayer assemblies in water and aqueous solution [Yager (1984) Mol. Cryst. Liq. Cryst. 106:371-381; Schnur (1993) Science 262:1669-1676; Selinger (2001) J. Phys. Chem. B 105:7157-7169]. One proposed application of lipid tubules is as vehicles for controlled drug release. Accordingly, such tubes coated with metallic copper and loaded with antibiotics were used to prevent marine fouling.
Although lipid-based nanotubules are simple in form, lipid structures are mechanically weak and difficult to modify and functionalize, thus restricting their range of applications.
Material sciences involve the understanding of material characteristics as well as the development of new materials. Industrial and academic needs encourage material scientists to develop new materials having superior mechanical, electrical, optical and/or magnetic properties for many applications. Modern material sciences focus on the investigation of polymers, ceramics and semiconductors in many fluidic as well as solid forms including fibers, thin films, material bulks and the like.
Various manufacturing processes are known in the art for making synthetic fibers. Many synthetic fibers are produced by extrusion processes, in which a thick viscous liquid polymer precursor or composition is forced through one or more tiny holes of a spinneret to form continuous filaments of semi-solid polymer. As the filaments emerge from the holes of a spinneret, the liquid polymer converts first to a rubbery state which then is solidified. The process of extruding and solidifying filaments is generally known as spinning.
Wet spinning processes are typically employed with fiber-forming substances that have been dissolved in a solvent. Wet spinning techniques are preferred for spinning of high molecular weight polyamides. The spinnerets forming the filaments are submerged in a wet chemical bath, and as the filaments of the fiber-forming substances emerge from the spinnerets, they are induced to precipitate out of the solution and solidify.
In gel spinning, the polymer is not in a true liquid state during extrusion. The polymer chains are bound together at various points in liquid crystal form. This produces strong inter-chain forces in the resulting filaments that can significantly increase the tensile strength of the fibers. In addition, the liquid crystals are aligned along the fiber axis by the shear forces during extrusion. The filaments emerge with high degree of orientation relative to each other, further enhancing the strength. Typically, in gel spinning, the filaments first pass through air and then cooled in a liquid bath.
In dry spinning, the polymer is dissolved in a volatile solvent and the solution is pumped through the spinneret. As the fibers exit the spinneret, air is used to evaporate the solvent such that the fibers solidify and can be collected on a take-up wheel.
In melt spinning the polymer is melted and pumped through the spinneret. The molten fibers are cooled, solidified, and collected on a take-up wheel. Stretching of the fibers in both the molten and solid states provides for orientation of the polymer chains along the fiber axis.
Dispersion spinning is typically employed when the polymer having and infusible, insoluble and generally intractable characteristics. In this technique, the polymer is dispersed as fine particles in a chemical carrier that permit extrusion into fiber. The dispersed polymer is then caused to coalesce by a heating process and the carrier is removed by a thermal or chemical procedure.
Reaction spinning processes involve the formation of filaments from pre-polymers and monomers. The pre-polymers and monomers are further polymerized and cross-linked after the filament is formed. The reaction spinning process begins with the preparation of a viscous spinning solution, which is prepared by dissolving a low molecular weight polymer in a suitable solvent and a reactant. The spinning solution is then forced through the spinneret into a solution or being combined with a third reactant. The primary distinguishable characteristic of reaction spinning processes is that the final cross-linking between the polymer molecule chains in the filament occurs after the fibers have been spun. Post-spinning steps typically include drying and lubrication.
In tack spinning, a polymeric material in a tacky state is interposed between a foundation layer and a temporary anchorage surface. Being in a tacky state, the polymeric material adheres to the foundation layer and the temporary anchorage surface. The foundation layer is then separated from the temporary anchorage surface to produce fibers of the polymeric material. The fibers are hardened by thermal or chemical treatment, and separated from the temporary anchorage surface.
In electrospinning, a fine stream or jet of liquid is produced by pulling a small amount of charged liquefied polymer through space using electrical forces. The produced fibers are hardened and collected on a suitably located precipitation device to form a nonwoven article. In the case of a liquefied polymer which is normally solid at room temperature, the hardening procedure may be mere cooling; however other procedures such as chemical hardening or evaporation of solvent may also be employed.
Other processes for manufacturing polymeric articles include film blowing and injection molding.
In film blowing, an extruder is used to melt the polymer and pump it into a tubular die. Air blown into the center of the tube causes the melt to expand in the radial direction. The melt in thus extended in both radial and down-stream direction. The formed film is then collected by an arrangement of rollers.
In injection molding, a reciprocating or rotating screw both melts polymer pellets and provides the pressure required to inject the melt into a cold mold. The cold mold provides the article the desired shape.
In the area of thin film production, a well-known method for producing and depositing monolayers is the Langmuir-Blodgett method. In this method a monolayer of amphiphilic molecules is formed at the surface of a tank filled with a liquid sub-phase such as water. Amphiphilic molecules are those having a hydrophobic first end and a hydrophilic second end lined up side by side in a particular direction. In the Langmuir-Blodgett method, a solution of amphiphilic molecules dissolved in a solvent which is not miscible with the sub-phase liquid in the tank is spread onto the liquid surface. When the solvent evaporates, a loosely packed monolayer is formed on the surface of the sub-phase. A transition of the monolayer thus formed from a state of gas or liquid to a solid state is then achieved by compressing surface area of the layer to a predetermined surface pressure. The resulting monolayer is deposited onto the surface of a substrate by passing the substrate through the compressed layer while maintaining the layer at a predetermined surface pressure during the period of deposition.
Another method for producing a monolayer is known as self-assembling of molecules. In this method, a monolayer film is generated as a result of adsorption and bonding of suitable molecules (e.g., fatty acids, organic silicon molecules or organic phosphoric molecules) on a suitable substrate surface. The method typically involves solution deposition chemistry in the presence of water.
Over the years, extensive efforts were made to develop row materials which can be used for manufacturing fiber and films by the above techniques to provide articles having enhanced and/or application-specific characteristics. For example, one of the most studied natural fibrillar system is silk [Kaplan D L, “Fibrous proteins—silk as a model system,” Polymer degradation and stability, 59:25-32, 1998]. There are many forms of silk, of which spider silk of Nephila clavipas (the golden orb weaver) is regarded as nature's high performance fiber, with a remarkable combination of strength, flexibility, and toughness. Although assembled by non-covalent interactions, silk is stronger than steel per given fibrillar diameter but, at the same time, is much more flexible. Due to its superior mechanical properties, the spider silk can be used in many areas requiring the combination of high mechanical strength with biodegradability, e.g., in tissue engineering applications [Kubik S., “High-Performance Fibers from Spider Silk,” Angewandte Chemie International Edition, 41:2721-2723, 2002].
A known method of synthesizing spider silk material includes the introduction of a spider silk gene into a heterologous gene expression system and the secretion of spider silk protein therefrom. The protein is then processed, typically by electrospinning, to produce a fiber of enhanced mechanical properties [Jin H J, Fridrikh S V, Rutledge G C and Kaplan D L, “Electrospinning Bombyx mori silk with poly(ethylene oxide),” Biomacromolecules, 3:1233-1239, 2002].
Recently, electrospinning has been employed to fabricate virus-based composite fibers hence to mimic the spinning process of silk spiders [Lee S and Belcher A M, “Virus-Based Fabrication of Micro- and Nanofibers Using Electrospinning,” Nano letters, 4:388-390, 2004]. In this study, M13 virus was genetically modified to bind conductive and semiconductor materials, and was thereafter subjected to an electrospinning process to provide conductive and semiconductor fibers.
Other than synthesized spider silk, the electrospinning process can be applied on a diversity of polymers including polyamides, polyactides and water soluble polymer such as polyethyleneoxide [Huang Z M, Zhang Y Z, Kotaki M and Ramakrishna S., “A review on polymer nanofibers by electrospinning and their applications in nanocomposites,” Composites Science and technology, 63:2223-2253, 2003]. Heretofore, about 50 types of polymers have been successfully electrospun.
Electrospinning has also been used with carbon nanotubes to obtain super-though carbon-nanotube fibers [Dalton A B et al., “Super-tough carbon-nanotube fibers—These extraordinary composite fibers can be woven into electronic textiles,” Nature, 423:703, 2003]. By modifying a familiar method for carbon nanotubes fibers [Vigolo et al., “Macroscopic Fibers and Ribbons of Oriented Carbon Nanotubes,” Science, 17:1331-1334, 2000] the researchers were able to spin a reel of nanotube gel fiber and then convert it into 100 m length of solid nanotube composite fiber. The resulting fibers were tougher than any other known natural or synthetic organic fiber. However, carbon nanotubes in general and carbon-nanotube fibers in particular suffer from structural deviations. Although deviations in structure can be introduced in a “controlled” manner under specific conditions, frequent uncontrollable insertion of such defects result in spatial structures with unpredictable electronic, molecular and structural properties. In addition, the production process of carbon nanotubes is very expensive and presently stands hundreds of U.S. dollars per gram.
Recently, peptide building blocks have been shown to form nanotubes. Peptide-based nanotubular structures have been made through stacking of cyclic D-, L-peptide subunits. These peptides self-assemble through hydrogen-bonding interactions into nanotubules, which in-turn self-assemble into ordered parallel arrays of nanotubes. The number of amino acids in the ring determines the inside diameter of the nanotubes obtained. Such nanotubes have been shown to form transmembrane channels capable of transporting ions and small molecules [Ghadiri, M. R. et al., Nature 366, 324-327 (1993); Ghadiri, M. R. et al., Nature 369, 301-304 (1994); Bong, D. T. et al., Angew. Chem. Int. Ed. 40, 988-1011 (2001)].
More recently, the discovery of surfactant-like peptides that undergo spontaneous assembly to form nanotubes with a helical twist has been made. The monomers of these surfactant peptides, like lipids, have distinctive polar and non-polar portions. They are composed of 7-8 residues, approximately 2 nm in length when fully extended, and dimensionally similar to phospholipids found in cell membranes. Although the sequences of these peptides are diverse, they share a common chemical property, i.e., a hydrophobic tail and a hydrophilic head. These peptide nanotubes, like carbon and lipid nanotubes, also have a very high surface area to weight ratio. Molecular modeling of the peptide nanotubes suggests a possible structural organization [Vauthey (2002) Proc. Natl. Acad. Sci. USA 99:5355; Zhang (2002) Curr. Opin. Chem. Biol. 6:865]. Based on observation and calculation, it is proposed that the cylindrical subunits are formed from surfactant peptides that self-assemble into bilayers, where hydrophilic head groups remain exposed to the aqueous medium. Finally, the tubular arrays undergo self-assembly through non-covalent interactions that are widely found in surfactant and micelle structures and formation processes.
Peptide based bis(N-α-amido-glycyglycine)-1,7-heptane dicarboxylate molecules were also shown to be assembled into tubular structures [Matsui (2000) J. Phys. Chem. B 104:3383].
When the crystal structure of di-phenylalanine peptides was determined, it was noted that hollow nanometric channels are formed within the framework of the macroscopic crystal [Gorbitz (2001) Chemistry 7(23):5153-9]. However, no individual nanotubes could be formed by crystallization, as the crystallization conditions used in this study included evaporation of an aqueous solution at 80° C. No formation of discrete nano-structures was reported under these conditions.
As mentioned hereinabove, peptide nanotubes contributed to a significant progress in the field of nanotechnology since such building blocks can be easily modified and used in numerous mechanical, electrical, chemical, optical and biotechnological systems.
The development of systems which include nanoscale components has been slowed by the unavailability of devices for sensing, measuring and analyzing with nanometer resolution. One class of devices that have found some use in nanotechnology applications are proximity probes of various types including those used in scanning tunneling microscopes, atomic force microscopes and magnetic force microscopes. While good progress has been made in controlling the position of the macroscopic probe to sub-angstrom accuracy and in designing sensitive detection schemes, the tip designs to date have a number of problems.
One such problem arises from changes in the properties of the tip as atoms move about on the tip, or as the tip acquires an atom or molecule from the object being imaged. Another difficulty with existing probe microscope tips is that they typically are pyramidal in shape, and that they are not able to penetrate small openings on the object being imaged. Moreover, existing probe microscopes often give false image information around sharp vertical discontinuities (e.g., steps) in the object being imaged, because the active portion of the tip may shift from the bottom atom to an atom on the tip's side.
An additional area in which nanoscience can play a role is related to heat transfer. Despite considerable previous research and development focusing on industrial heat transfer requirements, major improvements in cooling capabilities have been held back because of a fundamental limit in the heat transfer properties of conventional fluids. It is well known that materials in solid form have orders-of-magnitude larger thermal conductivities than those of fluids. Therefore, fluids containing suspended solid particles are expected to display significantly enhanced thermal conductivities relative to conventional heat transfer fluids.
Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids required in many industrial applications. To overcome this limitation, a new class of heat transfer fluids called nanofluids has been developed by suspending nanocrystalline particles in liquids such as water, oil, or ethylene glycol. The resulting nanofluids possess extremely high thermal conductivities compared to the liquids without dispersed nanocrystalline particles. Excellent suspension properties are also observed, with no significant settling of nanocrystalline oxide particles occurring in stationary fluids over time periods longer than several days. Direct evaporation of copper nanoparticles into pump oil results in similar improvements in thermal conductivity compared to oxide-in-water systems, but importantly, requires far smaller concentrations of dispersed nanocrystalline powder.
Numerous theoretical and experimental studies of the effective thermal conductivity of dispersions containing particles have been conducted since Maxwell's theoretical work was published more than 100 years ago. However, all previous studies of the thermal conductivity of suspensions have been confined to those containing millimeter- or micron-sized particles. Maxwell's model shows that the effective thermal conductivity of suspensions containing spherical particles increases with the volume fraction of the solid particles. It is also known that the thermal conductivity of suspensions increases with the ratio of the surface area to volume of the particle. Since the surface area to volume ratio is 1000 times larger for particles with a 10 nm diameter than for particles with a 10 mm diameter, a much more dramatic improvement in effective thermal conductivity is expected as a result of decreasing the particle size in a solution than can obtained by altering the particle shapes of large particles.
Since nanotubes have relatively straight and narrow channels in their cores, it was initially suggested that these cavities may be filled with foreign materials to fabricate one dimensional nanowires. Early calculations suggested that strong capillary forces exist in nanotubes, which are sufficient to hold gases and fluids inside them [Pederson (1992) Phys. Rev. Lett. 69:2689]. The first experimental proof was provided by Pederson and co-workers, who showed filling and solidification of molten leaf inside nanotubes [Pederson (1992) Phys. Rev. Lett. 69:415]. Various other examples, concerning the filling of nanotubes with metallic and ceramic materials exist in the literature [Ajayan (1993) Nature 361:392; Tsang (1994) Nature 372:416; Dujardin (1994) 265:1850].
Despite high applicability, the process of filling carbon nanotubes is difficult and inefficient. Most commonly produced carbon nanotubes, are capped at least at one end of the tube and no method for efficiently opening and filling the carbon nanotubes with foreign material is known to date. For example, nanotube ends can be opened by post oxidation treatment in an oxygen atmosphere at high temperature. The major drawback of such a procedure is that the tube ends become filled with carbonaceous debris. As a consequent, filling the open-ended tubes after post oxidation with other material has proven difficult. Another problem with carbon nanotubes synthesized in inert gas arcs is the formation of highly defective tubes containing amorphous carbon deposits on both the inside surface and outside surface of the tubes and the presence of discontinuous graphite sheets. Furthermore, since carbon nanotubes are curved, wetting may prove difficult. Finally, since the internal cavity of SWNTs is very small, filling can be done only for a very limited number of materials.
Some of the limitations plaguing the carbon based nanostructures and those made from other inorganic composites do not exhibit themselves in the nanostructure made from peptides described above. Nevertheless, although at least some of the above-described peptides were shown to form open-ended nanotubes [Hartgerink (1996) J. Am. Cham. Soc. 118:43-50], these are composed of peptide building blocks, which are relatively long and as such are expensive and difficult to produce, or limited by heterogeneity of structures that are formed as bundles or networks rather than discrete nanoscale structures.
The self-assembled peptide nanostructures are well ordered assemblies of various shapes with persistence length on the order of micrometers. The formation of the peptide nanostructures is very efficient and the nanostructures solution is very homogeneous. Similar to carbon nanotubes, the peptide nanostructures are formed as individual entities. For industrial applications, the self-assembled peptide nanostructures are favored over carbon nanotubes and spider silk from standpoint of cost, production means and availability.
It is recognized that improved peptide nanotubes are natural candidates for performing the above and many other tasks in the field of nanotechnology.
There is thus a widely recognized need for, and it would be highly advantageous to have, hollow and fibrillar peptide nanostructure and macroscopic and microscopic articles thereof, which are devoid of the above limitations.